Process and apparatus for the hydraulic impregnation of cellulosic materials



July 24, 1962 M. SUTHERLAND ETAL 3,

PROCESS AND APPARATUS FOR THE HYDRAULIC IMPREGNATION OF CELLULOSIC MATERIALS Filed June 1, 1959 INVENTORS LIONEL M. SUTHERLAND 8| THOMAS H. PARIS.

ATTORNEYS 3,646,183 Patented July 24, 1952 ice PRGCESS AND APPARATUS FOR TIE HY DRAULIC IMPREGNATION F CELLULOSIC MATERIALS Lionel M. Sutherland, Tequesta, Fla., and Thomas H. Paris, Trenton, N.J., assignors to Tomlon Corporation, Trenton, N.J., a corporation of New Jersey Filed June 1, 1959, Ser. No. 817,303 9 Claims. (Cl. 162--56) This invention relates to a process for impregnating cellulosic materials with cooking liquors by means of hydrostatic pressure. More particularly, it relates to a process in the manufacture of wood pulps wherein wood chips or billets are thoroughly impregnated with cooking liquor prior to digestion and further treatment.

In the process of manufacturing chemically treated Wood pulps, it is desirable that the cooking liquors shall contact all or substantially all of the constituent wood fibers of the chips or billets being treated. The problem of penetrating the fibers of wood chips or billets with cooking liquors is magnified by the presence of mixed species of wood, by the varying moisture content of the wood and by the varying characteristics of the cooking liquors themselves. Thorough penetration is highly desirable and facilitates the pulp making process. If the woody material is dry, penetration is retarded by the presence of air within the wood cells which forms a system of gas and liquid areas in the structural tubes through which penetration takes place. Penetration is aided by the use of wood chips of small dimensions. This however, requires expensive comminution facilities.

Chips which have not been thoroughly impregnated with liquid are subject to a high amount of structural damage when introduced into a continuous cooking apparatus by virtue of the force exerted by the continuous conveying means used for introducing the chips into the cooking device.

Where well cooked pulps are desired, especially those pulps requiring subsequent bleaching, use of the continuous cooking method is made impractical where less than thoroughly impregnated chips are to be treated since the continuous cooker does not allow sufficient retention time to permit thorough penetration of the complete chip by the cooking liquor and simultaneously to obtain a commercially acceptable rate of production.

Existing processes for the impregnation of cellulosic materials are of several general types, such as, for exarnple, the processes of steaming, soaking, alternate applications of vacuum and steam under pressure, or the like. All of the impregnation methods of the prior art require a lengthy treatment time which is not suitable for use in combination with a continuous cooking process where uniformly cooked pulps are desired. These former processes generally require impregnation times of from one to twelve hours, depending on the manipulative steps of the individual process.

It is an object of this invention to provide a rapid method for the thorough impregnation of cellulosic material with cooking liquors. It is a further object to provide a process which requires a short period of time in which to achieve full penetration. A further object is to provide a process by which cellulosic materials of mixed species are uniformly penetrated by the cooking liquor. A still further object is to provide a process and apparatus for carrying out the impregnation which may be readily integrated with continuous cooking systems and conventional batch type digesters. Another object is to provide an economical process of pretreating cellulosic materials which results in a uniformly treated pulp which may be rapidly digested in conventional cooking apparatus.

Other objects and advantages of this invention will become apparent from a reading of the following description and by referring to the drawing which illustrates a diagrammatic plan of a plan for impregnating cellulosic materials in accordance with the principles of this invention.

According to the specific embodiment of this invention, chosen for purposes of illustration, wood blocks, billets or chips or a mixture of them are removed from a storage bin 11 and conveyed by a conveyor 12 to the opening 13 of a pressure vessel 14. The pressure vessel 14 has top and bottom closures, 15, 16, these closures being operated by quick opening hydraulic cylinders 17, 18. Prior to the charging of wood chips into the vessel, bottom closure 16 is shut and the top closure 15 is opened. When a complete batch of the material to be treated has been charged, closure 15 is sealed. At this point, cooking liquor, at a temperature less than about 212 F., is introduced by pump 19 from supply tank 20 into the pressure vessel, thereby forcing air out of pressure vessel through line 23 and then through separator 24. When substantially all of the air has been displaced from the pressure vessel 14, pump 19 is stopped and a valve 30 in line 23 closed. A high pressure device 25 continues to admit cooking liquor into the pressure vessel 1%. Reverse flow through pump 19 is prevented by a check valve 29. The pressure required in order to fully impregnate the cellulosic material varies considerably with respect to the size of the pieces, the species of the material, the moisture content of the material and the characteristics of the cooking 1iquor utilized. It is generally known that thorough impregnation is a function of both time and pressure with the corollary that a higher pressure will result in a shorter treatment. In accordance with this invention, high pressures considerably higher than those generally employed in the art are produced by device 25 in order that the penetration time may be greatly shortened. It has been found that by using hydraulic pressures of from 500 to 2500 pounds per square inch that thorough impregnation is achieved within one minute or less, compared to the usual practice in sulphate cooking which requires from 45 minutes to 1 /2 hours and in sulphite cooking, requiring from 2 to 3 hours. Other cooking processes require as high as twelve hours for complete penetration of the cellulosic material.

When the chips have been completely impregnated, excess liquor drain 26 is opened and the cooking liquor returned to supply tank 2%, the pressure within vessel 14 thereby dropping to that of the atmosphere. Bottom closure 16 is now opened by means of quick operating hydraulic cylinder 18, permitting the impregnated chips to discharge into the chip storage bin 27, excess cooking liquor returning through screen 21 and conduit 22 into supply tank 20. Bottom closure 16 is now closed and the impregnation cycle repeated.

The thoroughly impregnated chips may be conveyed from storage bin 27 to a continuous digester 28. Alternatively the chips may be conveyed to a conventional digester where they may be cooked in the vapor phase (with no additional liquor) or may be flooded with cooking liquor in the normal manner as required.

The following example is an illustration of the application of the above specific embodiment of this invention.

Example 1 Wood from freshly cut and dry timber was charged into a pressure vessel. The maximum size of the pieces was approximately 4" diameter x 3" long. The vessel was filled with kraft cooking liquor at 212 F. and the pieces of wood were subjected to hydrostatic pressure of approximately 1200 pounds per square inch. This hydrostatic pressure was maintained for approximately 30 seconds, at the end of which time the charge of cooking Example 2 In accordance with the procedure of Example 1, wood from freshly cut and dry timber was thoroughly impregnated in approximately seconds while being subjected to hydrostatic pressure of approximately 2200 pounds per square inch.

Example 3 In accordance with the procedure of Example 1, wood from freshly cut and dry timber was thoroughly impregnated in approximately one minute while being subjected to hydrostatic pressure of approximately 600 pounds per square inch.

Likewise, in accordance with the principles of this invention, the rapid impregnation of Whole logs of Wood may be accomplished. The following example represents a suitable procedure for carrying out this embodiment of the invention.

Example 4 A debarked piece of dry solid wood approximately 3 inches in diameter and 10 inches long is placed in a pres- Sure vessel having hydraulic pressure resistant closures. The vessel is flooded with cooking liquor and sealed. Hydrostatic pressure of 2000 pounds per square inch is applied to the cooking liquor Within the vessel for approximately 30 seconds and then relieved. The piece of wood is removed, having received thorough impregnation with the cooking liquor.

The impregnation process and apparatus of this invention have many advantages. The use of this process perrnits the uniform pe etration of wood chips with cooking liquor, thereby overcoming a principal problem of continuous cooking systems. By virtue of this invention, the long time periods now required to achieve thorough impregnation of wood chips are obviated by this novel one step process whereby the supply of impregnated chips to a continuous cooking system can readily be made continuous itself, thereby increasing the productive capacity of continuous digesters. The production of batch type digesters is likewise improved by this process. Another advantage of this invention is the achievement of uniform penetration of both wet (freshly cut) and dry wood even in the presence of mixed wood species.

Another advantage arises in view of the fact that a high degree of wood utilization is obtained without the use of extraordinary comminution apparatus. For example, the reduction in size of wood scraps and waste which are usually discarded from lumbering and manufacturing operations,-such as furniture making and the like, is eliminated since large solid pieces of Wood can be readily thoroughly impregnated in a short time. When the process and apparatus of this invention are utilized in conjunction with a continuous digester, an inherent advantage is obtained since fully impregnated chips are less affected by the crushing action of the continuous conveying mechanism required to introduce material into continuous cookers. Still other advantages are the saving of steam, through a marked reduction in cooking time, the use of stronger cooking liquors, and the use of cooking liquors previously considered unsuitable because of their poor impregnation characteristics.

It is to be understood that the form of the invention disclosed herein is to be taken as a preferred embodiment. Various changes may be made in the process and apparatus of the invention. It is contemplated that the process and apparatus described herein may be automatically controlled so as to enable the utilization of a fully continuous pulp production system. Furthermore equivalent ele' ments may be substituted for those illustrated and described herein, elements may be reversed and certain features of the invention may be utilized independently of the use of other features, all without departing from the spirit or scope of the invention as defined in the subjoined claims.

Having thus described our invention, We claim:

1. A process for thoroughly impregnating cellulosic material with a cooking liquid comprising the steps of charging pieces of cellulosic material into a container; filling the container with a cooking liquid having a temperature of not more than about 212 F; closing said container; subjecting said cooking liquid and said pieces of cellulosic material to hydrostatic pressure within the container of at least 500 pounds per square inch; maintaining said pressure for not longer than about one minute; and discharging said pieces from said container.

2. The process of claim 1 wherein the hydrostatic pressure established within the container is within the range of from about 500 to about 2500 pounds per square inch.

3. The process of claim 2 wherein a hydrostatic pressure of about 1500 pounds per square inch is maintained for about thirty seconds.

4. The process of claim 1 wherein the liquid treating medium is sulfate cooking liquor.

5. The process of claim 1 wherein the liquid treating medium is a sulphite cooking liquor.

6. The process of claim 1 wherein the liquid treating medium is a neutral sulphite cooking liquor.

7. The process of claim 1 wherein the liquid treating medium is an alkaline cooking liquor.

8. The process of claim 1 wherein the liquid treating medium is an acid cooking liquor.

9. The process of claim 1 wherein the liquid treating medium is an organic cooking liquor.

References Cited in the file of this patent UNITED STATES PATENTS 115,740 Keegan June 6, 1871 1,771,598 Wells July 29, 1930 1,903,962 Dreyfus 1 Apr. 18, 1933 1,979,341 Olsen Nov. 6, 1934 

1. A PROCESS FOR THOROUGHLY IMPREGNATING CELLULOSIC MATERIAL WITH A COOKING LIQUID COMPRISING THE STEPS OF CHARGING PIECES OF CELLULOSIC MATERIAL INTO A CONTAINER; FILLING THE CONTAINER WITH A COOKING LIQUID HAVING A TEMPERATURE OF NOT MORE THAN ABOUT 212*F.; CLOSING SAID CONTAINER; SUBJECTING SAID COOKING LIQUID AND SAID PIECES 